addressing uncertainty in oil and natural gas industry greenhouse

Wt% C
∑
lbmole x lbmole C 12 lb C 1
i
Total
= × × ×
100 lbmole
total
lbmolei lbmole C MWTotal
This equates to 71.7% C, as shown in Table 5-6.
For each compound in the gas mixture, the uncertainty from this calculation is determined by applying
Equation 4-6, using the relative uncertainties of the lbmole i and MW Total . This is demonstrated for ethane.
UR ( e lWt ) % C= Urel ( ) × Urel ( ) = 5.22 + 3.73 = 6.41%
2 2 2 2
i mole%
i MW Total
The uncertainty associated with the wt% C of the mixture is calculated by applying Equation 4-4, using the
absolute uncertainties for the weight percent carbon of each molar compound.
∑
2
U ( abs) = U ( abs)
( %)
Wt%
∑ wt
U ( abs) = (0.0624× 53.96) + (0.0641× 10.16) + (0.0707× 7.62) + (0.0672×
0)
∑( wt%)
U ( abs) = 3.4704
∑( wt%)
3.4704
Urel ( ) = × 100% = 4.84%
∑( Wt %)
71.7339
2 2 2 2
The uncertainties associated with the composition are used in the following comparison of the emission
estimation methodologies for H 2 plants.
Uncertainty for H 2 Plant Emissions – Feedstock Rate Approach
(API Compendium Equation 5-8)
The CO 2 emissions can be calculated using the feedstock rate and carbon content, applying Equation 5-8 from
the API Compendium:
E
E
CO2
CO2
9
3×
10 scf
=
yr
lbmole
×
379.3
= 178,336 tonnes CO
2
feed
scf
/ yr
18.9 lb
×
lbmole
feed 0.7173 lb C 44 lb CO
×
×
feed lb feed 12 lb C
2
tonne
×
2204.62 lb
The CO 2 uncertainty is then calculated by applying Equation 4-6 and using the relative uncertainty values.
Urel ( ) = Urel ( ) + Urel ( ) + Urel ( )
Urel
CO
2
2
2 2 2
Feedstock rate MW feedstock C content feedstock
2 2 2
( )
CO
= 15 + 3.73 + 4.84 = 16.2%
Uncertainty for H 2 Plant Emissions – H 2 Production Approach
(API Compendium Equation 5-9)
A second approach for estimating emissions associated with a hydrogen plant is based on the H 2 production
rate rather than the feedstock rate. This approach applies the stoichiometric ratio of H 2 formed to CO 2
Pilot Version, September 2009 5-16